In many situations it is desirable to measure a blood pressure of a human being or an animal. Generally, measurement of a pressure existing, for example, in an elastic fluid conductor (for example a tube, a thin-walled pipe or a blood vessel) may be used in order to monitor, for example, the function of a pump or other process parameters.
The “blood pressure”, which is a vital parameter, is e.g. a transmural pressure at arterial vascular walls which results from a difference between an internal pressure and an external pressure of the vessel (or blood vessel). By a contraction of the heart and a simultaneous expulsion of blood from a left ventricle into the aorta, a pressure forms within an aortic arch (for example within the vessel) due to the incompressibility of the blood, said pressure propagating as a pressure wave (also known as a pulse wave) from the aorta to a periphery (of a human being or an animal) and resulting in a short-time change in the volume (or local change in the volume or change in the cross section) of a section of the vessel observed. In this context, one distinguishes, e.g., between a systolic and a diastolic blood pressure value, and defines them accordingly as a maximum (systolic) and a minimum (diastolic) vessel pressure in the course of a cardiac cycle.
Various methods of blood pressure measurement are already known. For example, U.S. Pat. No. 6,736,789 B1 describes a method and a device for blood treatment using a device for continuously monitoring the blood treatment performed outside the body. A blood pressure of a patient, or a quantity correlated with the blood pressure, is measured and compared with a predetermined limiting value. If the blood pressure measured, or its relative change, falls below the predetermined limiting value, a signal is created in order to interrupt the sequence of treatments. Continuous non-invasive measurement of the blood pressure is based on a determination of the propagation velocity or transmit time of the pulse waves created by the heart contractions of the patient and by the propagation through the arterial system. To determine the pulse wave velocity or transmit time, the blood treatment machine comprises an electrocardiograph as well as means for detecting the pulse waves at a location remote from the person's heart.
GB 2394178 A describes a method of calibrating a blood pressure monitoring apparatus. A blood pressure measuring apparatus is calibrated by measuring the blood pressure of a living organism while using a manometer. In addition, a reference transmit time of a blood pulse wave is measured which travels from the heart along a blood vessel to a region that is remote from the heart. An arrival of the blood pulse wave at the fingertip is detected by using a plethysmograph. A first measurement of a blood pressure and of a transmit time is used for creating a first calibration data point. That region of the body that is remote from the heart is then raised and lowered down starting from a position that is at the same level as the heart. A transmit time is measured for the raised and lowered-down position. Subsequently, a blood pressure difference is calculated between a state wherein the region is raised or lowered down. A transmit time difference between the raised and the lowered-down position is calculated, and a second data point is created from the calculated blood pressure difference and transmit time difference.
U.S. Pat. No. 7,029,447 B2 describes a device and a system for non-invasive measurement of a blood pressure of a patient. The method comprises the following steps: determining a mechanical heartbeat starting time from an impedance cardiography signal, detecting a heartbeat pulse arrival time at a peripheral location of the patient, computing a pulse wave transmit time from the heart to the peripheral location while using the mechanical starting time of the heartbeat and the heartbeat pulse arrival time, as well as calculating an estimated value of a blood pressure of the patient from the pulse wave transmit time.
U.S. Pat. No. 6,648,828 B2 describes a continuous, non-invasive method of measuring blood pressure while using impedance plethysmography. A blood pressure is measured while utilizing a pulse transmit time that may be taken by the blood volume pulse to propagate between two locations in an animal. Impedance plethysmography is used for detecting when the blood volume pulse occurs at a location. The plethysmograph may detect a thorax impedance to determine when the aorta heart valve opens, or it may detect an impedance at a location of an extremity of the animal. The occurrence of the blood volume pulse at a different location may be determined by means of impedance plethysmography or another technology, such as pulse oxymetry. Calculation of a heartbeat volume may be used for compensating for any deviation of the blood pressure that may be due to effects based on an expansibility of the blood vessel. A blood pressure monitor may periodically provide a reference blood pressure measurement that is used for calibrating the derivation of the blood pressure on the basis of the pulse transmit time.
U.S. Pat. No. 6,331,162 B1 describes a device for measuring a pulse wave velocity. The device comprises first and second plethysmograph sensors connected to a computer. The sensors are positioned on the back of a patient so as to record pulse waveform information at two locations along the thoracic aorta. In addition, an electrocardiogram of the patient is recorded. As soon as the pulse waveforms and the electrocardiogram waveform have been recorded, data that is noisy or comprises artefacts is excluded, and the pulse waveforms are determined utilizing the electrocardiogram data points. Subsequently, the signal-averaged pulse waveforms are analyzed to determine a foot of each waveform and to determine a foot-to-foot transmit time between the two sensors. A pulse wave velocity is subsequently determined by dividing the distance between the sensors by the foot-to-foot transmit time.
Further aspects with regard to blood pressure measurement are also described in KR 000100697211 BA and in KR 102006069032 AA.